Coating type magnetic recording media are widely used in the fields of the recording tape, video tape and flexible disc. These types of magnetic recording media have a layer structure comprising a nonmagnetic support having laminated thereon a magnetic layer containing ferromagnetic powder and a binder. With the development of an information-oriented society, higher levels of characteristics, e.g., electro-magnetic characteristics, running durability and running performance are required of the magnetic recording media. That is, the audio tape for recording and reproducing music is required to have a higher level of original sound-reproducing performance, and the video tape is required to have excellent electromagnetic characteristics, such as excellent original image-reproducing performance.
For these requirements, improvements have been done mainly from two aspects of the magnetic characteristics of the medium and the surface conditions of the medium.
With respect to the improvement of the magnetic characteristics of the medium, a magnetic recording medium comprising a magnetic layer having high coercive force was proposed as a magnetic recording medium capable of obtaining excellent electromagnetic characteristics. It is reported that excellent electromagnetic characteristics can be obtained in this magnetic recording medium by making the ratio of the coercive force of the magnetic layer (Hc) to the residual magnetic flux density (Br) (i.e., Hc/Br) from 560 to 1,240 kA/(T·m), and further making the coercive force of the magnetic layer (Hc) from 160 to 240 kA/m (e.g., refer to JP-A-2000-268343).
However, in the environment where high durability is required, such as the case of performing recording and reproduction with a magnetic head of higher revolution, it is difficult to ensure high durability by the improvement of the magnetic characteristics of a medium alone. In particular, in the equipment for high density recording in recent years, the number of revolutions of the magnetic head drum is increased, and the number of revolutions of the magnetic head of the digital video tape recorder is even 9,600 rpm or higher. Since this engine speed is a far tremendous velocity as compared with 1,800 rpm of the analog video tape recorder for consumer use and 5,000 rpm for business use, the sliding velocity of the magnetic recording medium and the magnetic head is great. Also, the advances in the linear tape systems promote the higher data transfer rate, resulting in the faster tape speed. All these advances require the durable coating on the magnetic recording media.
For the purpose of improving electromagnetic characteristics and increasing recording density, it has been tried to smooth the surface of a magnetic layer to thereby reduce the noise generated from a magnetic recording medium. For example, a magnetic recording medium characterized in that a support having a skewness (Rsk) of from −1 to 4 is used for smoothing the surface has been suggested (e.g., refer to JP-A-8-279135). However, the tribological property of the magnetic layer with a magnetic head or other sliding elements (e.g., a guide roller and the like) lowers when smoothing is advanced thoughtlessly. Accordingly, it was tried to provide convexities on the surface of the magnetic layer for keeping the tribological property (e.g., refer to JP-A-9-134515). However, contrary to the expectations, dropout attributable to the convexities became conspicuous with the increase of recording density. Therefore, surface wherein concavities were predominant over convexities (Rsk was negative) was designed (e.g., refer to JP-A-11-175951). Rsk is a statistic index of concavities and convexities, and that Rsk is smaller than 0 means concavities are predominant over convexities. However, with the latest improvement of recording density, it has been known that these concavities are the cause of noises or dropout. In addition, it has also been found that tribological property deteriorates due to smoothing of surface (the reduction of the number of convexities).